An 11s hub body can accomodate all the cassette speed
varieties. Using less than 11s simply requires eating up the additional
hub body space using spacers not occupied by a cassette. 11s hubs are a
fairly universal system to accomodate nearly all cassettes you'd likely
encounter. Exceptions to this rule are Campagnolo cassettes, and SRAM
XD driver cassettes. Campy cassettes and XD driver cassettes are NOT
compatible.